People are living longer than ever and the demand for organ and tissue replacement has never been greater. Because of this, a key issue that researchers in the biomaterials field face today is biocompatibility, in particular blood compatibility, of artificial implants in human bodies. Protein adsorption followed by cell adhesion and various undesirable biological responses occurs when most foreign objects contact body fluid. Designing surfaces that proteins do not adsorb to and that cells do not adhere to is the primary approach in improving biocompatibility of artificial implants. Two strategies for designing compatible artificial implants have emerged and are worth noting: incorporation of poly(ethylene glycol) to surfaces, designing biomembrane-like surfaces containing phospholipids or phospholipid-like moieties. These strategies work in certain cases, but the weaknesses in the current approaches are: (1) the lack of stability of the modified implants during long term application and (2) the lack of fundamental structure-biocompatibility relationships. The objective of the work proposed here is to address these weaknesses by using surface chemistry to design long-lasting biocompatible implants by chemically bonding poly(ethylene glycol) (PEG) and phosphorylcholine (PC) groups to poly(ethylene terephthalate) (PET) surfaces. Surface grafting of epoxide-terminated PEG on two amine-containing surfaces and surface cationic polymerization of ethylene oxide on PET-OH surfaces are two proposed methods to introduce PEG with controllable chain length and density to PET substrates. PC groups will also be introduced to PET surfaces. This is a completely new strategy for improving the biocompatibility of PET implants. To quantify the amount of PEG and PC on PET substrates, three surface characterization techniques will be used: contact angle, x-ray photoelectron spectroscopy, and attenuated total reflectance infrared spectroscopy. We will correlate surface structural information with surface properties by assessing the protein adsorption and cell adhesion behavior of variable chain length and density PEG- and PC-containing surfaces.